Meaning of "Cogito ergo sum": short simple explanation

Cogito, ergo sum is a Latin phrase meaning“I think, therefore I am”. Used by French philosopher René Descartes in the Discourse on Method (1637), the formula has a variant in his work in 1641, in  Meditations : ego sum, ego existo ("I am, I exist" ). For Descartes it expresses the first certainty which resists a methodical doubt.. Seeking to completely rebuild knowledge, Descartes wishes to find a solid foundation, absolutely certain. This research leads him to the conclusion that only his own existence, as a "thing that thinks", is initially certain. It is this discovery that the "cogito" expresses. Regardless of the formulations, the cogito constitutes a major element of Cartesian thought. There is a certainty from which Descartes will attempt to rebuild all knowledge. It consists of an intuition that is not limited to a logical deduction.